1. Field of the Invention
This invention generally relates to a gas sensor. This invention relates to, for example, a gas sensor located in an exhaust system of an automotive internal combustion engine for measuring a specific-component concentration such as an oxygen concentration in an exhaust gas produced by the engine.
2. Description of the Related Art
FIG. 1 shows a prior-art gas sensor which includes a sensor element 920 inserted into a housing. An atmosphere-side cover is provided on the housing. An insulator 93 is provided in the housing. The insulator 93 has terminal accommodation holes 930 and 931. Two metal terminals 94 are placed in each of the terminal accommodation holes 930 and 931.
As shown in FIG. 2, each of the metal terminals 94 has a connecting portion 941 and a resilient contact portion 940. The resilient contact portion 940 is designed and formed as a leaf spring. The insulator 93 has ribs 91 providing insulation between the metal terminals 94 in the terminal accommodation hole 930 and the metal terminals 94 in the terminal accommodation hole 931.
A base end of the sensor element 920 is disposed in an element accommodation hole 92 formed among the metal terminals 94. As the sensor element 920 is placed in position, the sensor element 920 meets and then resiliently deforms the resilient contact portions 940 of the metal terminals 94. In this way, terminal electrodes of the sensor element 920 and the resilient contact portions 940 of the metal terminals 94 are brought into contact with each other. The deformation of the resilient contact portions 940 provides reliable electric contact between the metal terminals 94 and the terminal electrodes of the sensor element 920.
As the prior-art gas sensor in FIG. 1 is miniaturized, the size of the insulator 93 decreases and the element accommodation hole 92 among the metal terminals 94 narrows. In some cases, the metal terminals 94 are close to or in contact with each other before the sensor element 920 is placed in position.
With reference to FIG. 3, as the sensor element 920 is inserted into the insulator 93, the sensor element 920 meets the resilient contact portions 940 of the metal terminals 94. Then, the sensor element 920 is further pushed into the insulator 93 by a strong force, deforming and moving the resilient contact portions 940 of the metal terminals 94 away from each other along directions xe2x80x9caxe2x80x9d. Thus, a sufficient gap is formed between the resilient contact portions 940 of the metal terminals 94. The sensor element 920 moves through the region between the resilient contact portions 940 of the metal terminals 94 while sliding on and contacting with them.
The sensor element 920 is made of fragile material such as ceramic. Thus, the sensor element 920 tends to be damaged when being pushed against the resilient contact portions 940 of the metal terminals 94 by the strong force.
It is conceivable to thicken the sensor element 920 to increase its stiffness. Also, it is conceivable to increase the original distance between the metal terminals 94. In these cases, the body size of the prior-art gas sensor is large.
It is conceivable to reduce the spring performances of the resilient contact portions 940 of the metal terminals 94. In this case, the sensor element 920 can be placed in position with a weaker force. On the other hand, wrong electric contact tends to occur between the sensor element 920 and the resilient contact portions 940 of the metal terminals 94.
Thus, it is difficult that the prior-art gas sensor in FIG. 1 is miniaturized while reliable electric contact is provided between the sensor element 920 and the metal terminals 94.
It is an object of this invention to provide a small-sized gas sensor in which reliable electric contact is provided between a sensor element and a metal terminal (or metal terminals).
A first aspect of this invention provides a gas sensor comprising a housing having a base end; a sensor element inserted into the housing and fixed with respect to the housing, the sensor element having a base end; terminal electrodes provided on the base end of the sensor element; an atmosphere-side cover provided on the base end of the housing; an insulator provided in the atmosphere-side cover and having terminal accommodation holes, the insulator having an element accommodation hole in which the base end of the sensor element is placed, the element accommodation hole communicating with the terminal accommodation holes, the insulator having ribs forming inner surfaces defining the element accommodation hole, the ribs having a thickness smaller than a thickness of the base end of the sensor element; leads for electrical connection with an external; metal terminals at least partially placed in the terminal accommodation holes respectively and having connecting portions connected with the leads, the ribs being located between the metal terminals to form spaces between the metal terminals; wherein as the base end of the sensor element is placed in the element accommodation hole, the terminal electrodes on the base end of the sensor element come into contact with the metal terminals so that the terminal electrodes are electrically connected with the leads via the metal terminals.
A second aspect of this invention is based on the first aspect thereof, and provides a gas sensor wherein the metal terminals include the connecting portions connected with the leads, and resilient contact portions which are resiliently deformable, the resilient contact portions being in contact with the ribs while being resiliently deformed.
A third aspect of this invention is based on the first aspect thereof, and provides a gas sensor wherein the metal terminals have projections in contact with the terminal electrodes on the base end of the sensor element.
A fourth aspect of this invention is based on the first aspect thereof, and provides a gas sensor wherein the ribs include ribs for locating the metal terminals, and ribs for providing insulation between the metal terminals.
A fifth aspect of this invention is based on the second aspect thereof, and provides a gas sensor wherein the metal terminals have shoulders between the connecting portions and the resilient contact portions, the shoulders including bends at right angles.
A sixth aspect of this invention is based on the second aspect thereof, and provides a gas sensor wherein in each of the metal terminals, a central line of the connecting portion and a central line of the resilient contact portion are out of alignment.
A seventh aspect of this invention is based on the first aspect thereof, and provides a gas sensor wherein the base end of the sensor element has a taper portion.
An eighth aspect of this invention is based on the first aspect thereof, and provides a gas sensor wherein the ribs extend between the terminal accommodation holes.
A ninth aspect of this invention is based on the first aspect thereof, and provides a gas sensor wherein the insulator is fixed with respect to the atmosphere-side cover.
A tenth aspect of this invention provides a gas sensor comprising a housing having a base end; a sensor element inserted into the housing and fixed with respect to the housing, the sensor element having a base end; at least one terminal electrode provided on the base end of the sensor element; an atmosphere-side cover provided on the base end of the housing and having a base end and a front end; a resilient insulating member provided on the base end of the atmosphere-side cover and having at least one first insertion hole; an insulator provided in the front end of the atmosphere-side cover and having at least one second insertion hole; a lead placed in the first insertion hole; and a metal terminal placed in the second insertion hole and having a connecting portion electrically connected with the lead and a resilient contact portion electrically connected with the terminal electrode on the base end of the sensor element; wherein the resilient insulating member includes a first guide portion defining a front end of the first insertion hole and restricting motion of the lead, and the insulator includes a second guide portion defining a base end of the second insertion hole and restricting motion of the metal terminal.
An eleventh aspect of this invention is based on the tenth aspect thereof, and provides a gas sensor wherein the metal terminal includes a leaf spring.
A twelfth aspect of this invention is based on the tenth aspect thereof, and provides a gas sensor wherein the second guide portion has a length in a range of 1 mm to 5 mm.
A thirteenth aspect of this invention is based on the tenth aspect thereof, and provides a gas sensor wherein there are provided a plurality of the second guide portions, and a distance between centers of the second guide portions is in a range of 3 mm to 6 mm.
A fourteenth aspect of this invention is based on the tenth aspect thereof, and provides a gas sensor wherein the first guide portion has a length in a range of 3 mm to 8 mm.
A fifteenth aspect of this invention is based on the tenth aspect thereof, and provides a gas sensor wherein the insulator has at least one rib adjacent to the second insertion hole, the rib having a thickness smaller than a thickness of the sensor element, the metal terminal being in contact with the rib while being contracted in a radial direction of the insulator, and wherein the base end of the sensor element is placed in an element accommodation space formed between the rib and the metal terminal.
A sixteenth aspect of this invention is based on the tenth aspect thereof, and provides a gas sensor wherein the metal terminal has a projection in contact with the terminal electrode on the base end of the sensor element.
A seventeenth aspect of this invention is based on the tenth aspect thereof, and provides a gas sensor wherein there are provided a plurality of the ribs and a plurality of the metal terminals, the ribs including ribs for locating the metal terminals and ribs for electrically insulating the metal terminals from each other.
An eighteenth aspect of this invention is based on the tenth aspect thereof, and provides a gas sensor wherein the metal terminal has a shoulder between the connecting portion and the resilient contact portion, the shoulder including a bend at right angles.
A nineteenth aspect of this invention is based on the tenth aspect thereof, and provides a gas sensor wherein a central line of the connecting portion of the metal terminal and a central line of the resilient contact portion thereof are out of alignment.
A twentieth aspect of this invention is based on the tenth aspect thereof, and provides a gas sensor further comprising a metal member electrically connecting the metal terminal and the lead.
A twenty-first aspect of this invention is based on the twentieth aspect thereof, and provides a gas sensor wherein the first guide portion restricts motion of the metal member.
A twenty-second aspect of this invention is based on the twentieth aspect thereof, and provides a gas sensor wherein the metal member is inserted into the first guide portion.
A twenty-third aspect of this invention is based on the tenth aspect thereof, and provides a gas sensor wherein the atmosphere-side cover contains an internal space located between the resilient insulating member and the insulator, and the atmosphere-side cover has a hole communicating with the internal space for introducing atmosphere into the internal space.
A twenty-fourth aspect of this invention is based on the tenth aspect thereof, and provides a gas sensor wherein the insulator has an atmosphere introduction passage.